C# 8 开关内的表达式

Question

I'd like to be able to call a method/local function from within the new C# switch expression pattern matching.

Here's an example I've got:

        string result = value switch
        {
            IsFizz(value) => "Fizz",
            IsBuzz(value) => "Buzz",
            (IsFizz(value) && IsBuzz(value)) => "FizzBuzz",
            _ => value.ToString()
        };

However I get the follow errors:

A single-element deconstruct pattern requires some other syntax for disambiguation. It is recommended to add a discard designator '_' after the close paren ')'.

Sytnax error, '=>' expected

Invalid expression term '&&'

Is it not possible to use new the switches in this manner?

Answer 1

Yes, but in the when clause:

        string result = value switch
        {
            _ when IsFizz(value) => "Fizz",
            _ when IsBuzz(value) => "Buzz",
            _ when (IsFizz(value) && IsBuzz(value)) => "FizzBuzz",
            _ => value.ToString()
        };

(shouldn't the FizzBuzz test come first?)